1. Filed of the Invention
This invention relates to novel ester group-containing tertiary amine compounds which are useful as additives for novel chemical amplification resists suitable for fine processing techniques.
2. Description of the Related Art
While increasingly finer pattern rules are required as the degree of integration and speed of LSIs become higher, far ultraviolet lithography is regarded as a promising fine processing technique of the next generation. Far ultraviolet lithography is capable of processing down to a size of 0.2 μm or less, and when a resist material having low light absorption is used, permits the formation of patterns having sidewalls substantially perpendicular to the substrate. Moreover, a technique using a high luminance KrF excimer laser as the light source of far ultraviolet radiation is attracting attention in recent years. In order to employ this technique as a mass production technique, a resist material having low light absorption and high sensitivity is desired.
From this point of view, chemically amplified positive resist materials using an acid as the catalyst have recently been developed (as disclosed, for example, in Japanese Patent Publication No. 2-27660/'90 and Japanese Patent Provisional Publication No. 63-27829/'88). These resist materials have excellent characteristics such as high sensitivity, high resolution and high dry etching resistance, and are hence particular promising for use in far ultraviolet lithography.
One disadvantage of chemically amplified resists is that, if the resist is allowed to stand for a long time between light exposure and PEB (Post Exposure Bake), the formed line patters have a T-top shape, i.e. the patterns have a thickened upper part (this problem is referred to as PED (Post Exposure Delay)). Another disadvantage is the so-called footing phenomenon in which the lower part of the patterns is thickened in the neighborhood of the substrate especially when the substrate comprises a basic material such as silicon nitride or titanium nitride. It is considered that the T-top phenomenon is due to a reduction in the solubility of the resist film at the surface, and the footing phenomenon on the substrate surface is due to a reduction in the solubility of the resist film in the neighborhood of the substrate. Moreover, a problem arises in that a dark reaction eliminating an acid-labile group proceeds during a period of time extending from light exposure to PEB, resulting in a reduction in line dimensions.
These problems present serious drawbacks when chemically amplified resists are put to practical use. Owing to these drawbacks, conventional chemically amplified positive resist materials have been unsatisfactory in that dimensional control is difficult not only in lithographic steps but also in substrate processing by dry etching (see, for example, W. Hinsberg et al., J. Photopolym. Sci. Technol., 6(4), 535–546(1993); and T. Kumada et al., J. Photopolym. Sci. Technol., 6(4), 571–574(1993)).
In chemically amplified positive resist materials, the problems of PED and footing on the substrate surface are considered to be closely related to basic compounds present in air or on the substrate surface. The acid formed in the surface of the resist film by exposure to light is inactivated by reaction with basic compounds in air. As the standing time till PEB is prolonged, the amount of acid inactivated increases and, therefore, the acid-labile group becomes hard to decompose. Consequently, a hardly soluble layer is formed at the film surface and the patterns assume a T-top shape.
It is well known that the addition of a basic compound suppresses the influence of basic compounds in air and is hence effective against PED (U.S. Pat. No. 5,609,989, WO 98/37458, Japanese Patent Provisional Publication No. 63-149640/'88, Japanese Patent Provisional Publication No. 5-113666/93, Japanese Patent Provisional Publication No. 5-232706/'93 (U.S. Pat. No. 5,580,695) and Japanese Patent Provisional Publication No. 5-249662/'93 (U.S. Pat. No. 5,968,712 and 20010038964)).
Well-known basic compounds are nitrogen-containing compounds such as amine compounds and amide compounds having a boiling point of 150° C. or above. Specific examples thereof include polyvinylpyridine, aniline, N-methylaniline, N,N-dimethylaniline, o-toluidine, m-toluidine, p-toluidine, 2,4-lutidine, quinoline, isoquinoline, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, 2-pyrrolidone, N-methylpyrrolidone, imidazole, α-picoline, β-picoline, γ-picoline, o-aminobenzoic acid, m-aminobenzoic acid, p-aminobenzoic acid, 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, 2-quinolinecarboxylic acid, 2-amino-4-nitrophenol, and triazine compounds such as 2-(p-chlorophenyl)-4,6-trichloromethyl-s-triazine. Among them, pyrrolidone, N-methylpyrrolidone, o-aminobenzoic acid, m-aminobenzoic acid, p-aminobenzoic acid and 1,2-phenylenediamine are especially preferred.
These nitrogen-containing compounds are weak bases, and can mitigate the T-top problem. However, when a highly reactive acid-labile group (e.g., an acetal group such as 1-ethoxyethyl) is used, it is impossible to control the reaction, i.e., the diffusion of the acid. The addition of a weak base has been disadvantageous especially in that the dark reaction during PED proceeds in unexposed regions and causes a reduction in line size (slimming) and a film loss at the line surface in the case of an acetal-derived acid-labile leaving group. In order to solve these problems, it has been effective to add a strong base. However, it may not be definitely said that a compound having a higher basicity is more effective. In fact, the addition of so-called superstrong bases such as DBU (1,8-diazabicyclo[5.4.0]-7-undecene), DBN (1,5-diazabicyclo[4.3.0]-5-nonene), proton sponge, and quaternary amines (e.g., tetramethylammonium hydroxide) has failed to produce a sufficient effect.
The effects produced by the addition of a basic compound to a resist composition include not only an improvement in environmental stability, but also an enhancement in resolution. The addition of a base reduces sensitivity, but enhances contrast in acid release. In exposed regions where the number of moles of the acid released is smaller than the number of moles of the base added, the acid is inactivated by neutralization with the base, and is unable to cause a catalytic reaction. However, as soon as the neutralization point is exceeded, an acid is suddenly released to cause a catalytic reaction.
The phenomenon of sudden acid release induced by the addition of a base in the vicinity of the neutralization point was called a proton jump by Hatakeyama et al. (SPIE Symp. Proc., 3333, 62(1998)). Moreover, Hatakeyama et al. carried out a close investigation on the mechanism of a proton jump and proposed a competitive reaction theory that the neutralization reaction between the acid formed by exposure to light and the base takes place at the same time as the reaction catalyzed by the acid occurs (J. Photopolymer. Sci. Technol., Vol. 13(4), p. 519(2000)). They solved kinetically the neutralization reaction between the acid formed photochemically and the base added, and showed that a base having a greater reaction rate constant can give higher contrast.